General Relativity: Curved Spacetime and Its Tests
Gravity is treated as the curvature of spacetime rather than as a force, starting from the observation that free fall and weightlessness cannot be told apart. Light bending, orbit precession and clock rates are the tests.
What a learner can do afterwards
- States the equivalence principle and gives an experiment it explains
- Describes gravitational time dilation and its effect on satellite navigation
- Names the classical tests of the theory and what each one measured
1 · Read
The equivalence principle says gravity and acceleration feel identical in a small sealed room. An astronaut in free fall feels weightless, exactly as in deep space far from any mass. Einstein concluded that gravity is not a force pulling through space but the shape of spacetime itself.
Picture light crossing a falling elevator: to riders inside, the beam bends. Gravity must bend light paths too. Planets and dropped balls simply follow the straightest available paths through curved spacetime.
Three early measurements made the theory convincing. Mercury creeps forward slightly more than Newton predicts, starlight grazing the Sun deflects by the predicted angle, and light climbing out of gravity reddens. Each measures curvature doing the work.
Stronger gravity also slows the pace of time, so clocks on navigation satellites tick differently than ground clocks. Position fixes would drift within a day unless receivers correct for it. Gravity bends both paths and clocks.
Mass curves spacetime, objects follow the curves, and clocks in the curves run slow.
2 · Watch
Take it off screen
Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.